Conventionally, x-ray computed tomography (CT) (x-ray tomography), magnetic resonance imaging (MRI), positron emission tomography (PET), and other methods are used to visualize information on the interior of an object such as a biological body and a building. Specifically, electromagnetic waves such as light, terahertz waves, millimeter waves, and microwaves, or phonon-like waves such as ultrasonic waves, sound waves, and elastic waves are radiated to a biological body or an object that is to be observed, or are radiated to plasma, and resultant scattered waves (reflected waves) are observed and analyzed to visualize information on the interior of the biological body, the interior of the object, or the interior of the plasma. Recently, instead of waves, an electromagnetic field is also used to visualize information on the interior of a biological body or an object.
Generally, these methods adopt a technique in which waves u such as electromagnetic waves or ultrasonic waves are radiated to an object O, scattered waves p that are waves scattered by the object O are observed in multiple places around the object O, and resultant data is visualized (for example, refer to Patent Literatures (PTLs) 1 to 3 and Non Patent Literatures (NPLs) 1 to 3).
In the technique disclosed in PTL 1, information on the interior of an object is visualized using radio waves. For the visualization, data on scattered waves observed with a sensor arranged on the circumference of a circle is repeatedly obtained while the data is modified using a parameter such as electrical conductivity or a dielectric constant.
The technique disclosed in PTL 2 is the ultrasound phased array technique. In this technique, data on ultrasonic waves received by an ultrasonic sensor is modified using a mean vector and is visualized.
In the technique disclosed in PTL 3, ultrasonic waves are radiated in a plane to an object to visualize data on ultrasonic waves received by a sensor. Information on the interior of an object in a curved shape is visualized using an increased number of observed data items or using approximation or modification, for example.
The technique disclosed in NPL 1 is a technique related to a multi-path linear array radar and allows information on a flaw or the like inside concrete to be visualized. In this technique, a sensor is arranged on a surface of an object to observe scattered waves of radiated waves, and observed data is analyzed and visualized.
The technique disclosed in NPL 2 allows information on the interior of an object to be visualized using ultrasonic waves. In this technique, scattered waves are observed when ultrasonic waves are radiated to an object, and observed data is visualized by way of the Born approximation (the Kirchhoff Approximation).
In the technique disclosed in NPL 3, scattered waves obtained by a sensor arranged on a curved surface are observed, and time waveform data obtained for each sensor is compared with previously obtained data and is visualized.